Azerbaijan is reportedly poised to buy advanced military aircraft from Russia in addition to billions of dollars worth of other Russian-made weapons acquired in the past several years.

The Azerbaijani news agency APA reported on Tuesday that Moscow has agreed to supply an unspecified number of Yak-130 trainer and light attack jets to Baku. “We think Azerbaijan will, in the near future, be among the countries that are using Yak-130 aircraft,” it quoted a spokesman for their state-run manufacturer, Irkut, as saying.

According to APA, Azerbaijani military pilots started learning to fly Yak-130s and familiarizing themselves with their characteristics last year.

Yak-130 was designed in the early 1990s and went into service with the Russian Air Force in 2009. Primarily designed as an advanced training aircraft, it is equipped with a cannon, missiles and bombs allowing it to carry out attack and reconnaissance missions.

The reported sale of Yak-130s follows a series of large-scale defense contracts which Russia has signed with Azerbaijan, a country locked in a bitter conflict with Moscow’s main regional ally, Armenia. Russian and Azerbaijani officials have estimated the total volume of those contracts signed since 2010 at nearly $4 billion.

The Armenian government, which is heavily reliant on Russian military aid, has until now been careful not to openly criticize the Russian arms supplies to Baku. Still, President Serzh Sarkisian voiced concern at them earlier this month. “It is a very painful subject and our people are worried that our strategic ally sells weapons to Azerbaijan,” Sarkisian said in a newspaper interview. Defense Minister Seyran Ohanian made similar comments on the subject afterwards.

The Armenian Defense Ministry on Wednesday declined to comment on the planned delivery of Russian jets to Azerbaijan. The ministry spokesman, Artsrun Hovannisian, only cited the statements made by Sarkisian and Ohanian.

For its part, Nagorno-Karabakh’s ethnic Armenian leadership said that the reported Yak-130 deal is no cause for concern. Davit Babayan, the spokesman for Karabakh President Bako Sahakian, argued that Yak-130 is primarily used as a trainer. “If I’m not mistaken, Armenia too has such aircraft,” he told RFE/RL’s Armenian service (Azatutyun.am).

Babayan also dismissed growing concerns in Yerevan over the broader Russian-Azerbaijani military cooperation. “This is pure business,” he said.

Armenian politicians and pundits believe, however, that the Russian-Azerbaijani arms deals are strengthening Baku’s hand in the Karabakh conflict and increasing the likelihood of another Armenian-Azerbaijani war. “This is inadmissible,” said Stepan Safarian, an opposition figure leading a newly established think-tank in Yerevan. “I think that Armenia must hold Russian-Armenian consultations and demand explanations because in essence Russia is acting against the logic of strategic partnership [with Armenia] and the principles of conflict mediation.”